Missing cosmic lithium shows up in a neighboring galaxy

Study solves one problem, creates another: is lithium made other ways?

The Small Magellanic Cloud (SMC), one of the Milky Way's satellite galaxies. Because the SMC contains relatively fewer metals (elements heavier than helium), astronomers were able to measure the amount of lithium in the galaxy more precisely than before.

An early success of the Big Bang model was the prediction of the primordial amounts of hydrogen and helium, a product of the first formation of atoms, known as the Big Bang nucleosynthesis (BBN). However, BBN predicts roughly four times more lithium than we've seen in the atmospheres of stars.

Lithium is far harder to create in stars than elements such as carbon, oxygen, and the like. Therefore, most of the lithium present in the Universe today was created in approximately the first three minutes after the Big Bang, with the balance being made by high-energy cosmic rays. (That's right: your gadgets run on a remnant of the Big Bang.) Thus, the missing lithium has been a minor problem for BBN, leading to some speculation about where it might be found.

Cosmologists may be able to rest a little easier: new observations of interstellar gas in the Small Magellanic Cloud (SMC) have measured a lithium abundance consistent with BBN. The SMC (a satellite galaxy of the Milky Way) contains a lot fewer heavier nuclei than the Milky Way, meaning its chemical composition is closer to that of the early Universe.

In addition to observations, astronomers J. Christopher Howk, Nicolas Lehner, Brian D. Fields, and Grant J. Mathews calculated the amount of lithium that should be present in interstellar gas. Since their observational results are so close the predictions of BBN, they actually lead to new problems: explaining why stars have less lithium than expected, and where the lithium produced via cosmic rays could have gone.

Most atoms in the Universe are hydrogen or helium; any heavier elements, known perversely by astronomers as metals, were almost all made via nuclear fusion in stars or supernovae. (The Big Bang, hot as it was, couldn't sustain fusion during inflation, so very little fusion happened after about 5 minutes.) Lithium is awkwardly in between the light elements and metals. It tends to be destroyed in stellar cores, so the BBN was responsible for most of the lithium present in the Universe today, according to widely accepted models.

Figuring out how much lithium was formed during the BBN is a relatively simple calculation, requiring just the ratio of ordinary matter (as opposed to dark matter) to photons in the early Universe. That number is very well constrained by the cosmic microwave background (CMB). Modern lithium abundances are calculated using a combination of BBN and cosmic ray levels (high-energy protons can smash into helium atoms, creating lithium), and a tiny amount lost through destruction by stars.

To test whether these calculations were right, previous observations concentrated on the outer layers and atmospheres of old stars, which are low in metal content. However, these observations found far too little lithium, meaning either BBN required correction from physics beyond the Standard Model, or some process affected the amount of lithium in stars.

If the latter is true, looking at something other than stars should reveal the missing lithium. Which is why the researchers were looking at the gas in the SMC.

Interstellar gas again is mostly hydrogen and helium, but in environments like the Milky Way, generations of stars have enriched it with metals. The SMC, on the other hand, is metal-poor, so the chemical makeup of the gas it contains should more closely reflect the primordial abundances. Another advantage to viewing the SMC is its proximity—since it orbits the Milky Way, it's relatively easy to observe individual stars.

The researchers looked at a particular supergiant star and measured how its light was absorbed by intervening gas along the line of sight. This gave them the lithium abundance, which isn't the absolute number of atoms present, but the relative number compared to hydrogen or other elements. In this case, the authors calculated the expected fraction of lithium nuclei compared with potassium and iron.

Combining the calculations with observational data, the researchers found the best fit was the predictions of BBN alone, without contributions from stars or cosmic rays—a somewhat puzzling result. They postulate that perhaps a smaller amount of primordial lithium might exist due to deviations from basic BBN, meaning the cosmic ray production could raise it to the levels we see, but that introduces a kind of fine-tuning problem, where we arbitrarily tweak models to get the results we see.

The hope now is that further observations may be able to constrain alternatives to the simplest form of BBN (which might involve extensions to the Standard Model), or see what other mechanisms might exist to produce lithium.

23 Reader Comments

I think there will probably be a straightforward explanation of why the SMC has primordial lithium. First, Stars don't just not produce lithium, they burn it. Second, the main cause of cosmic rays is supposed to be from shock fronts produced by supernova explosions. In other words, they're primarily a local phenomenon in a galaxy. If the SMC is a starburst going through it's first generation of stars, as suggested by the near primordial lithium abundance, you would expect neither a significant enrichment from cosmic rays nor the significant depletion you would expect if a large fraction the interstellar gas had been cycled through stars.

It is good news that they find lithium high enough concentrations. Having both later sources and sinks, I wouldn't worry too much about the exact amount, and see it as in need of finetuning due to forcing all possible mechanisms in. As BlackGriffen notes, we don't know too much about CR in the first place, that is my impression anyway.

As for lithium observations of stars, I would guess there are many models predicting what is seen. I remember one I've seen (because it had swedish authors), which managed to predict the observations comfortably. I wouldn't know, but having the generic BBN problem licked as far as magnitude goes, the star models could come down to picking and choosing what works best.

I don't want to detract from this important find, but IMHO the big cosmological news now would be the Milky Way core X-ray haze and the local source seen, all fitting dark matter.

If LHC doesn't see hints of supersymmetry in its quark-gluon interactions in the upcoming years, predicting a lowest energy supersymmetric WIMP dark matter candidate, I would now be very surprised. And eternal inflation needs supersymmetry too. [/crows]

Not to drift too far off topic, but could increased amounts of lithium in the SMC lead to lower incidences of bipolar depression there?

Didn't seem to work too well for Kurt Cobain. You see the problem is that, just like Kurt, the SMC has plenty of lithium available, but it's not consuming it. Might want to avoid standing behind the SMC just in case.

I'm a little lost on this one. Perhaps someone with a bit more background in this field can help me out? I knew there was an issue with not being enough lithium in the galaxy. Fair enough. Is this article stating, that we found the a whole lot of lithium in another galaxy? How exactly does that explain the missing lithium in our own galaxy?

I'm a little lost on this one. Perhaps someone with a bit more background in this field can help me out? I knew there was an issue with not being enough lithium in the galaxy. Fair enough. Is this article stating, that we found the a whole lot of lithium in another galaxy? How exactly does that explain the missing lithium in our own galaxy?

It implies that the post-BB development of metals was uneven. Instead of a consistent development of metals, there were areas of differential development in the first few minutes; the local galaxy was in a zone that didn't develop much lithium, but the SMC was in a higher-development region.

Lithium is the least of my worries. My question is: what was before the Big Bang?

That depends on how you define Big Bang. Since the current inflationary standard cosmology places an inflation period before the earlier theory, it makes most sense to call the overall expansion process big bang and these models big bang models.

The idea of an initial and helpfully local singularity was only ever an appended hypothesis that was expected to fully constrain a presumed Theory Of Everything. Inflation pushes those singularities, who remains, onto the inflation physics so in a sense what was before the earlier big bang model is already answered: inflation.

If you want to go deeper and take our cosmology's inflation physics seriously, the Planck energy cutoff isn't determining the global physics. Which, I believe, is what you see in GRB photon timing, and if supersymmetry exists, polarization. If you trust those observations, and some pushes above the required 3 sigma for hypothesis testing, spacetime is still smooth below Planck scales, the fluctuations in the CMB is only fluctuations originating in the original inflation ("inflaton") field.

I suppose that is what string theory predicts when it maps high energy physics onto low energy physics by way of dualities, a smooth sailing. Maybe expansion goes "all the way down = all the way up" in this physics.

According to Susskind et al, anthropic theory makes any initial condition irrelevant, if not known to be unnecessary as of yet. I.e you no longer need an initial low entropy, say by fluctuation, and conversely any fluctuation problems (Boltzmann Brains) go away. In eternal inflation a past eternal multiverse is the basic physics, if Susskind et al are correct. A typical observer has 0 likelihood to observe the transients from any beginning.

The cosmological arrow of time is then due to a fractal flow attractor around a dominant vacuum and future terminal vacuums of the flow, instead of due to initial singularities, initial low entropy and/or ongoing expansion. ["Fractal-Flows and Time's Arrow", Susskind, arxiv 2012.]

The interesting thing is now "what will be after the Big Bang (expansion)"? I'm reading Bousso's et al work where they predict our universe has ~ 5 billion more years to go before thermalization, and a 50 % risk the universe vacuum ends before another 3 billion years...

Yeah, I don't get the physics of terminal vacuums either, yet. The LHC seems to agree that our vacuum is quasistable though, if the ~ 125 GeV boson is a standard Higgs and no other physics appears. So our fiery end is certainly not anything new in that sense, in today's physics it will happen, inflation or no inflation.

Lithium is the least of my worries. My question is: what was before the Big Bang?

Old model: God create time, therefore before God created the world, there was no time.

Einstein model: Before the Big Bang, time did not exist therefore: the question is bad.

Inflation model: Like Einstein, but super-rapid expansion in the first few minutes.

Chaotic Inflation model: Same shit BUT there are these chaotic bubbles that give birth to NEW universes, infinitely arising - we're in one of those bubbles

White Hole model: The other side of a black hole is a white hole and our universe is a white hole spewing energy out the other end, and in fact this loops infinitely and all black holes are like this with white holes on the other side that are "universes"

Big Bounce model: Like Inflation mode, but eventually the universe reverses and we have a Big Crunch where everything smooshes back into a tine singularity smaller than a quark before having another Big Bang.

Branes - this is the superstring theory of the universe looping infinitely - big 2d membranes called branes collide and form energy and particles giving birth to "us" - it's really way more complex so you can research branes and superstring theory if you want to know more

I believe that covers all major theories of what's before the Big Bang.

Lithium is the least of my worries. My question is: what was before the Big Bang?

An open bar, mountain of coke, and a sleazy producer named Dick Hard.

Best explanation, by far.

More seriously though, I prefer to categorize such questions as pertaining to "Physics" (in the classical sense of it being a catchall for the sciences, or that which can be observed) or "Metaphysics" (which is literally "beyond" physics, or that which cannot be observed). This question, "what was before the Big Bang?" is obviously of the later category, and I've personally found it a waste of time to try to answer Metaphysical questions at all because there may never be a way to determine if you're right or wrong about it.

I'm a little lost on this one. Perhaps someone with a bit more background in this field can help me out? I knew there was an issue with not being enough lithium in the galaxy. Fair enough. Is this article stating, that we found the a whole lot of lithium in another galaxy? How exactly does that explain the missing lithium in our own galaxy?

This is similar to Gold or Diamond deposits around the Earth. Why are there heavier concentrations of each in specfic areas and other areas have little or completely lack any deposit ?

Diamond deposits all over Africa. US territory has a couple.

Gold concentrations all over N. and S. America - much fewer around the rest of the planet.

Why aren't both more evenly concentrated around the planet ?

Nature has nothing to do with balancing out a nice neat math equation. -- that is the first thing oyu have to get past for an answer to your question.

Otherwise there wouldn't be extinction - every point on the globe would be a comfy 78° all year round - more evenly distributed earthquakes - hurricanes - volcanos - tornados - monsoons.

I believe that covers all major theories of what's before the Big Bang.

Except that "white holes" have been rejected because it was later realized the physics doesn't work, and very few think "bounce" theories work either for similar reasons.

Over at Cosmic Variance there is a guest post by Tom Banks, a critic of eternal inflation. If you read his paper that he links to, it seems those who work with string theory, which would be the majority of theoretical physicists, work on eternal inflation. Or at least that the field of the string landscape, which is the string main theory on how it works, is dominated by it.

More seriously though, I prefer to categorize such questions as pertaining to "Physics" (in the classical sense of it being a catchall for the sciences, or that which can be observed) or "Metaphysics" (which is literally "beyond" physics, or that which cannot be observed). This question, "what was before the Big Bang?" is obviously of the later category, and I've personally found it a waste of time to try to answer Metaphysical questions at all because there may never be a way to determine if you're right or wrong about it.

Modern cosmology says you are wrong, we can predict and test such processes as multiverses. As the cosmological constant only comes out of eternal inflation, we know that there is a multiverse and that the observed end of inflation was only local.

I would say that metaphysics is philosophy, which doesn't pass the outsider's test. You can find as many schools and ideas that you have philosophers, they can't agree on something approaching facts. So it is a meaningless field, and it certainly has nothing to do with reality or science.

Zak wrote:Lithium is the least of my worries. My question is: what was before the Big Bang?

With a single atom?

We knew that human and all living things started out with a single cell and then it multiples into billion of cells. So it's obvious this was the same happened to the Universe it was also started out with a single thing which most likely it was a single atom, and when this single atom got irritated by something (don't know what that was) and exploded and bursted into billions of stars and galaxy. And everthing else in the universe is a history.

What was before a single atom that's what I want to know, and how it got "irritated", and irritated "from what"? :-)

Zak wrote:Lithium is the least of my worries. My question is: what was before the Big Bang?

With a single atom?

We knew that human and all living things started out with a single cell and then it multiples into billion of cells. So it's obvious this was the same happened to the Universe it was also started out with a single thing which most likely it was a single atom, and when this single atom got irritated by something (don't know what that was) and exploded and bursted into billions of stars and galaxy. And everthing else in the universe is a history.

What was before a single atom that's what I want to know, and how it got "irritated", and irritated "from what"? :-)

That "irritation" and "from what" I would like to know also.

Um... What?

Did you just take biology and apply it to physics? Did you just suggest that nucleosynthesis is similar to mitosis?

While "before the Big Bang" is a reasonable (if nonsensical under some interpretations) question, your "answer" just boggles my mind...

There is more to the Big Bang than just the appearance of matter. Space, as in the actual dimensions in which we reside are also in question when talking about cosmological origins. As such, your "obvious" idea that a single atom was "irritated" and "exploded", is severely lacking.